1. Field of the Invention
The present invention relates generally to light modulators, and more particularly, to a hybrid light modulator which includes a plurality of ribbons each having a plurality of protrusions to diffract incident light from an early light receiving stage and to control a diffractive angle of the light beam using a microactuator, thereby realizing the miniaturization of a device and assuring the ease of digital operation, unlike conventional diffractive optical modulators in which incident light is reflected and diffracted by the operation of a plurality of micromirror actuators.
2. Description of the Related Art
Generally, an optical signal processing technology has advantages in that a great amount of data is quickly processed in a parallel manner unlike a conventional digital information processing technology in which it is impossible to process a great amount of data in real time. Studies have been conducted on the design and production of a binary phase only filter, an optical logic gate, a light amplifier, an image processing technique, an optical device, and a light modulator using a spatial light modulation theory. The spatial light modulator is applied to optical memory, optical display device, printer, optical interconnection, and hologram fields, and studies have been conducted to develop a display device employing it.
The spatial light modulator is embodied by a reflective deformable grating light modulator 10 as shown in FIG. 1. The modulator 10 is disclosed in U.S. Pat. No. 5,311,360 by Bloom et al. The modulator 10 includes a plurality of reflective deformable ribbons 18, which have reflective surface parts, are suspended on an upper part of a substrate 16, and are spaced apart from each other at regular intervals. An insulating layer 11 is deposited on the silicon substrate 16. Subsequently, a sacrificial silicon dioxide film 12 and a low-stress silicon nitride film 14 are deposited. The nitride film 14 is patterned by the ribbons 18, and a portion of the silicon dioxide film 12 is etched, thereby maintaining the ribbons 18 on an oxide spacer layer 12 by a nitride frame 20. In order to modulate light having a single wavelength of λo, the modulator is designed so that thicknesses of the ribbon 18 and oxide spacer 12 are each λo/4.
Limited by a vertical distance (d) between a reflective surface 22 of each ribbon 18 and a reflective surface of the substrate 16, a grating amplitude of the modulator 10 is controlled by applying a voltage between the ribbon 18 (the reflective surface 22 of the ribbon 18 acting as a first electrode) and the substrate 16 (a conductive layer 24 of a lower side of the substrate 16 acting as a second electrode). In its undeformed state, with no voltage application, the grating amplitude is λo/2, and a total round-trip path difference between light beams reflected from the ribbon and substrate is one wavelength λo, and thus, a phase of reflected light is reinforced. Accordingly, in its undeformed state, the modulator 10 acts as a plane mirror when it reflects light. In FIG. 2, reference numeral 20 denotes incident light and reflected light in its undeformed state.
When a proper voltage is applied between the ribbon 18 and substrate 16, the electrostatic force enables the ribbon 18 to be moved downward toward a surface of the substrate 16. At this time, the grating amplitude is changed to λo/4. The total round-trip path difference is a half of a wavelength, and light reflected from the deformed ribbon 18 and light reflected from the substrate 16 are subjected to destructive interference. The modulator diffracts incident light 26 using the interference. In FIG. 3, reference numerals 28 and 30 denote light beams diffracted in a +/− diffractive mode (D+1, D−1) in a deformed state.
It has been proved that sticking between the ribbon 18 and substrate 16 is a gross problem of such a device during a wet process applied to form a space under the ribbon 18 and during operation of the modulator 10.
In an effort to overcome the above-mentioned problems, a conventional improved technology is proposed in Korean Patent Application No. 10-2000-7014798, entitled “method and a device for modulating an incident light beam to form a 2-D image”, by Silicon Light Machines Inc.
In the “method and device for modulating the incident light beam to form the 2-D image”, the diffractive grating light valve includes a plurality of elongate elements each having a reflective surface. The elongate elements are arranged on an upper side of a substrate so that they are parallel to each other, have support ends, and their reflective surfaces lie in array (GLV array). The elongate elements form groups according to display elements. The groups alternately apply a voltage to the substrate, resulting in deformation of the elements. The almost planar center portion of each deformed elongate element is parallel to and spaced from the center portion of the undeformed element by a predetermined distance which is set to ⅓–¼ of the distance between the undeformed reflective surface and the substrate. Thus, the deformed elongate elements are prevented from coming into contact with the surface of the substrate. Sticking between the elongate elements and the substrate is prevented by preventing contact between the elements and substrate. Additionally, the predetermined distance between each deformed elongate element and the substrate is limited so as to prevent hysteresis causing deformation of the elongate elements.
FIG. 4 is a side sectional view of an elongate element 100 of a GLV in an undeformed state according to a conventional improved technology. In FIG. 4, the elongate element 100 is suspended above a surface of a substrate (including constitution layers) by ends thereof. In FIG. 4, reference numeral 102 denotes an air space.
FIG. 5 is a plan view of a portion of the GLV including six elongate elements 100. The elongate elements 100 have the same width and are arranged parallel to each other. The elongate elements 100 are spaced close to each other, so that the elongate elements 100 can be deformed independently from other elements.
FIG. 6 is a front view of a display element 200 having undeformed elongate elements 100. FIG. 6 is a view taken in the direction of the arrows along the line A–A′ of FIG. 5. The undeformed state is selected by equalizing a bias on the elongate elements 100 to a conductive layer 106. Since reflective surfaces of the elongate elements 100 are substantially co-planar, light incident on the elongate elements 100 is reflected.
FIG. 7 is a front view of the display element 200 in which the deformed elongate elements 100 are alternately arranged. FIG. 7 is a view corresponding to FIG. 6, but showing the deformed elongate elements 100. The elongate ribbons 100 which are not removed are maintained at desired positions by an applied bias voltage. Deformation of the moving elongate ribbons 100 is achieved by alternate applications of operation voltages through the conductive layer 106 to the elongate elements 100. A vertical distance (d1) is almost constant to the almost planar center part 102, thereby limiting the grating amplitude of the GLV. The grating amplitude (d1) may be controlled by adjusting an operation voltage on the operated elongate elements 100. This results in precision tuning of the GLV in an optimum contrast ratio.
However, the light modulator which is manufactured by Silicon Light Machines Inc. and adopts an electrostatic method to control the position of a micromirror is disadvantageous in that an operation voltage is relatively high (usually 30 V or so) and a correlation between the applied voltage and displacement is nonlinear, and thus, reliability is poor in the course of controlling light.
Conventional light modulators disclosed in the patent filed by Bloom et al. have been used to form structures which display images. At this time, in each light modulator, two neighboring elements form one pixel. Of course, three neighboring elements may form one pixel. Alternatively, four neighboring elements may form one pixel. As a further alternative, six neighboring elements may form one pixel. In the case that a display device has an optical system which detects only diffracted light, when no voltage is applied to elements, such as ribbons, the ribbons are maintained in those original positions. At this time, pixels are dark, that is, are in a state of being turned off. Otherwise, when voltage is applied to the ribbons, the ribbons are warped downwards toward the silicon substrate. At this time, the pixels are bright, that is, attain a state of being turned on. A contrast ratio between a dark pixel and a bright pixel is a significant factor in forming the display system. In addition, an important matter in forming the display system is to accommodate the recent trend of miniaturization and high integration of electronic products.
However, the conventional light modulators disclosed in the patent filed by Bloom et al. have reached the limit in miniaturization. In other words, the conventional light modulators cannot be reduced under 3 μm in the width of the element. Furthermore, an interval between neighboring elements cannot be reduced under 0.5 μm.